1. Field of the Invention
The present invention relates to a steering control system for use in a moving vehicle, and more particularly to a steering control system for use in a moving vehicle such as a moving automobile, an unmanned mobile and carrying device in a factory, or an automated vehicle for use in agriculture, civil engineering machinery and the like.
2. Description of the Prior Art
Heretofore, as a system for detecting the current position of a moving body such as one of the moving vehicles described above, there has been proposed a system provided with a means for scanning a light beam emitted from the moving body in the circumferential direction or every azimuthal directions around the moving body, retroreflective means for reflecting to return the light beam in the direction of incident light which are secured at at least three positions apart from the moving body, and a beam receiver means for receiving light reflected from the retroreflective means (Japanese Patent Laid-open No. 67476/1984).
In the above mentioned prior art, differential azimuths between adjoining two of three retroreflective means around the moving body, or included angles formed by the adjoining two of three retroreflective means with the moving body are detected on the basis of received beam output of the light-receiving means, and the position of the moving body is calculated based on the detected differential azimuths and positional information of the retroreflective means which have been previously set.
In the above described system, however, there has been instances where the light beam emitted from a beam source mounted on the moving vehicle could not be directed to the retroreflective means positioned at reference points because of an inclination or vibration of the moving vehicle, or where the light-receiving means on the moving vehicle receives light reflected from objects other than the expected retroreflective means.
When real reflected light is not positively received by a light-receiving means, the position of the moving vehicle is erroneously calculated so that the moving vehicle cannot be traveled along a prescribed course.
Meanwhile, there has been proposed a method for detecting positions of the moving body which is so arranged that the scanning rate and scanning angle of the light beam are allowed to change, thereby positively directing the light beam to the retroreflective means; for example, Japanese Patent Laid-open No. 104503/1984. Furthermore, Japanese Patent Laid-open No. 211816/1984 proposes a system for detecting positions of the moving body which is so arranged that incident light produced on the moving body is converted into intermittent and periodical light, whereby the reflected incident light is discriminate from the light emitted from another light source.
In contrast to those, when retroreflective means are set in four positions, even if one of them is temporarily missed, the position of the moving body can be calculated on the basis of the positions of the remaining three retroreflective means and the direction of the missing retroreflective means can be reversely calculated from the calculated result (U.S. Patent application Ser. No. 454,824 now U.S. Pat. No. 5,019,990).
In addition, if retroreflective means are set only in three positions, it is also possible that, based on the data of the light-receiving direction of the retroreflective means detected in the previous scan cycles, the light-receiving direction in which the retroreflective means is to be detected during the next cycle is predicted, and the received light signal detected in the predicted direction is discriminated from the reflected lights from other objects and judged to be the light from the expected retroreflective means. According to this method, if no received light signal is detected in the predicted direction, the problem due to temporary missing of retroreflective means can be solved by directly using the predicted direction as the reflected light from the expected retroreflective means for the calculation of the self-position of the moving vehicle.
The above mentioned prior arts involve such problems that the system constructions become complicated, for example, the prior method which changes the scanning rate and angle of the light beam is required to vary frequently driving current in an optical scanner, and the prior system which is adapted to produce intermittent and periodical incident light is required to provide a complicated beam source section for producing the incident light.
In either prior art, there has been such a further problem that the position of the moving vehicle cannot be detected where there are troubles in a photosensor system such as a light-receiving means and retroreflective means, or where there are troubles in a rotary table driving section for revolving the photosensor system such as the light-receiving means and the like, or where some or all of the retroreflective means from which the reference signals used for calculation have tilted over.
Furthermore, there has been such a problem that the reflected light cannot be positively received by a moving vehicle because of contamination on a reflecting surface of retroreflective means, or the unexpected appearance of an obstruction when a person or other substance goes across the retroreflective means, as well as obstacles due to inclination or vibration of the moving vehicle. In this respect, these problems as mentioned above could not have been solved by only the above described prior arts.
If the moving vehicle is traveling in a straight line the problem of temporary missing of retroreflective means can be overcome by the above described prior art. However, if the moving vehicle is traveling on a course consisting of straight traveling courses and turning courses contiguous thereto and perform a planned work, there are the following problems.
First, since the direction of the retroreflective means is detected as an azimuth based on a predetermined reference line, for instance, the advance direction of the moving vehicle, the self-position of the moving vehicle can not be accurately calculated on the basis of the azimuth in the turning courses where the advance direction of the moving vehicle largely and quickly changes.
Second, since the rate of change in azimuth is large, if a retroreflective means has been missed, the calculation error undesirably becomes too great in the approach in which, based on the azimuth (direction) having been predicted in the latest detection cycle on the basis of the azimuth detected in the past, the azimuth in which the retroreflective means is to be detected in the current cycle is further predicted.
Accordingly, hitherto, in a turning course, the moving vehicle travels with the steering angle being fixed, and the fixing of the steering angle is released when the azimuth of the retroreflective means substantially coincide with a predetermined value and a straight traveling course is entered. However, once a retroreflective means has been missed, the reflected light from the retroreflective means would have largely changed in direction from the last azimuth even if it is detected again in the next scan cycle, and thus it is difficult to discriminate it from other incident lights from other objects and to accurately obtain, by relying on the azimuth, the timing for releasing the fixing of the steering angle to enter a straight traveling course. Consequently, counter measures for the missing of retroreflective means often needed to be taken also in a turning course, but application of only the above-mentioned prior art as the counter measures has been insufficient.